Field of the Invention
The present invention relates to an organic light emitting display (OLED) device, and more particularly, to an OLED device with improved thermal reliability.
Discussion of the Related Art
For an image display device which displays a variety of information on a screen as a core technology in advanced information and communication, there is continuous progress in development of slim, light-weight, and portable devices with improved performance. Hereupon, an organic light emitting display (OLED) device for controlling light intensity of an organic light emitting layer is recently receiving attention as a flat panel display device, along with demand for a flexible display capable of being bent pursuant to convenience and space utilization.
The OLED device can have a slim structure, include devices formed on a flexible substrate such as a plastic substrate, and be driven at a lower voltage, for example, at 10 V or less, than voltages required for a plasma display panel or an inorganic electroluminescent display, thereby reducing power consumption. In addition, much attention has been paid to OLED devices, since they are light-weight and realize high color quality.
Particularly, OLED devices are classified into active matrix organic light emitting display (AMOLED) devices and passive matrix organic light emitting display (PMOLED) devices. An AMOLED device displays an image using pixels including red, green, and blue sub-pixels arranged in a matrix form. Each sub-pixel includes an organic light emitting device and a cell driving unit that drives the organic light emitting device.
The cell driving unit includes at least two thin film transistors (TFTs) and a storage capacitor which are connected among a gate line supplying a scan signal, a data line supplying a video data signal, and a common power line supplying a common power signal to drive a first electrode of the organic light emitting device.
The organic light emitting device includes a first electrode, an organic light emitting layer, and a second electrode sequentially stacked and emits light using binding energy generated via combination of electrons and holes introduced into the organic light emitting layer by applying an electric filed to the first and second electrodes. The organic light emitting layer includes a host and a dopant and emits red, green, and blue light according to the types of the dopant and the host. The OLED device embodies full color emission by red, green, and blue sub-pixels respectively emitting red, green, and blue light.
However, if a host of the organic light emitting layer has a low glass transition temperature (Tg), quality of colors realized by the sub-pixels may be deteriorated by heat generated during emission of the organic light emitting device and operation of the TFT.
If a host has a low glass transition temperature, properties of the host change by heat to deteriorate quality of colors. Accordingly, color coordinates are partially changed to reduce a color reproduction rate. Particularly, when a host of a red organic light emitting layer has a lower glass transition temperature than those of green and blue organic light emitting layers so as to be vulnerable to heat, color purity and emission intensity of a red sub-pixel are relatively reduced. Thus, an OLED panel that realizes white light by mixing light emitted by red, green, and blue sub-pixels emits bluish green light instead of white light. As a result, reliability of the OLED device is reduced.